In bidirectionally transmitting and receiving DC power such as charging and discharging of a storage battery, a bidirectional DC/DC converter has been required and a large number of such bidirectional DC/DC converters have also been developed so far.
For example, Japanese Patent Laying-Open No. 2002-165448 (Patent Document 1) discloses an isolation-type bidirectional DC/DC converter as below. Namely, in FIG. 1 of Patent Document 1, down-converted power feed from a main battery 1 to an auxiliary machinery battery 5 is achieved as follows. As a pair of NMOS transistors 211 and 214 and a pair of NMOS transistors 212 and 213 are alternately turned on in a prescribed cycle, a single-phase rectangular wave AC voltage is generated. This single-phase rectangular wave AC voltage is down-converted by a transformer 3, the resultant voltage is subjected to single-phase full-wave rectification by a switching & rectification unit 41 and smoothening by a secondary-side smoothing circuit 42, and the resultant voltage is applied to auxiliary machinery battery 5. Meanwhile, up-converted power feed from auxiliary machinery battery 5 to main battery 1 is achieved as follows. By turning on both of NMOS transistors 411 and 412 of switching & rectification unit 41, magnetic energy is stored in a choke coil 421. Then, NMOS transistor 41 is turned off. Thus, an output voltage from auxiliary machinery battery 5 is up-converted through NMOS transistor 412 so that an AC voltage component is generated in a primary coil of transformer 3. Then, this AC voltage component is subjected to full-wave rectification by a flywheel diode D of a single-phase inverter circuit 21 and smoothing by a primary-side smoothing circuit 22, whereby main battery 1 is charged.